In cellular wireless systems channel state information is used for adaptation of the wireless link in order to more efficiently utilize the available bandwidth. For example if a channel is noisy it may only support a smaller transport block size and/or modulation and coding schemes that offer less data throughput as compared to the channel being less noisy, assuming there is a minimum performance metric (such as for example block error rate) as is the case with most cellular technologies. Channel state information is used generically and encompasses but is not limited to specific measures such as channel quality indication (CQI), precoding matrix indicator (PMI), rank indicator (RI), and the like.
In further advancements of the evolved universal terrestrial radio access network (E-UTRAN, also termed long term evolution LTE or 4G) there is research into a new downlink control channel. Whereas legacy E-UTRAN systems use a physical downlink control channel PDCCH for sending scheduling information to the user equipments (UEs), there are discussions of utilizing an enhanced PDCCH (ePDCCH) for that scheduling information. The PDCCHs and ePDCCHs are to schedule for the UEs radio resources on one or more physical downlink or uplink shared channels (PDSCH or PUSCH) on which the UEs receive or send their respective substantive data.
The ePDCCH is being developed to be more flexible in connection to signaling overhead as compared to the legacy PDCCH. Channel state information represents control signaling overhead that takes away from the radio resources available for substantive data, and so is justified to the extent it enables greater efficiencies for the substantive data sent on the PDSCH for example. For example, in the downlink the LTE network access node eNodeB is not able to obtain the downlink channel quality of a UE directly by itself, and so the UE measures it and reports it to the eNodeB which then adapts its downlink signaling to maximize downlink throughput on the PDSCH given the downlink channel conditions reported by the UE.
There are discussions in the development of the LTE-Advanced system (which is expected to be incorporated into Release 11 of 3GPP) for new requirements for the channel state information reporting concerning the ePDCCH, both in terms of the reporting mechanisms and the associated signaling needed to support these. The teachings below may be employed to advantage in this context, but are not limited only to channel state information for the ePDCCH of the LTE-Advanced system and may be used with any other wireless radio technology which uses link adaptation.